Uninflammable balloon



NOV. 20, 1934. J LETOURNEUR 1,981,600

UN I N FLAME-(TABLE BALLOON Filed Aug. 26, 1931 2 Sheets-Shet 1 ii? wayNov. 20, 193.4. J. LETOURNEUR MABLE BALLOON UNINFLAM 2 Sheets-Sheet 2Filed Aug. 26, 1951 1 Wm n5 2 J Patented Nov. 29, 1934 UNITED STATESUNINFLAMIiIABLE BALLOON Jean Letourneur, Versailles, France ApplicationAugust 26, 1931, Serial No. 559,467 In France September 19, 1930 8Claims.

The main danger occurring in the use of balloons lies in theinflammability of the gas used for their inflation. Amongst the gasesemployed for that purpose helium alone is uninflammable, but thescarcity of the known sources of this gas and the difficulties presentedby its extraction are such that the present production of helium isquite insufficient to meet the requirements of aerostation. It istherefore necessary usually to resort to other gases, such as hydrogen,notwithstanding the danger attending their use.

Such danger however may be considerably reduced and done away with inpractice by using two envelopes: one which is the gas envelope properlyso-called which contains a light but inflammable gas, and another whichentirely surrounds the first, whilst the space included between the twoenvelopes is inflated with a gas which causes no reaction with theoxygen of the air and with the light inflating gas. Hereinafter said gasis designated under the name of inert gas. If said gas is lighter thanair it naturally imparts to the complex its ascensional power. In thiscase therefore helium can be employed with. much advantage and, failingthe same, use may be made of nitrogen or any other inert gas or mixtureof gases, but in this case the question of lightness is only secondaryand the main property to be sought is that it should be inert in thesense above given to this term. If it is then supposed that a balloonconstructed in the abovementioned manner is pierced by a burning object,as, for instance, an incendiary projectile, it is easy to understandthat the ignition of the balloon will be avoided. As a matter of fact,the gas escaping into the atmosphere through the inlet and outlet holesof the outer envelope cannot become inflamed because it is inert.Likewise, the light gas which escapes through the inlet and outlet holesthrough the inner envelope is also incapable of catching fire, becauseit escapes into an atmosphere of inert gas with which there is noreaction. It is of course necessary that the thickness of the protectivelayer of inert gas should be suiflcient. Such thickness must bedetermined by previous experiments according to the nature and the sizeof the burning object or the projectile, the contact of which with theballoon is dangerous, the nature of the inflating gas, the nature of theinert gas, the use for which the balloon is intended, theclimate of theregions where the balloon is intended to be used, etc. Hereafter in thespecification the term thickness limit of the protective layer will beapplied to the smallest layers producing the protection desired.

But, in application, this fundamental device is difficult to realizecorrectly. In fact, it is necessary that at each instant during theascension, and at each point of the balloon, the thickness of the layerof inert gas should be at least equal to the thickness limit. Now, owingto the rising and falling motions of the balloon and the changes in theouter temperature, the volume of the gases, light and inert, undergoimportant variations, and the envelopes which hold them experienceconsiderable modifications in their forms, which it is generallydiflicult to control, so as always to comply with the essentialcondition of the aforesaid minimum thickness.

The object of this invention is to produce bal-' icons with a doubleenvelope in which the thickness of the protective layer of inert gasalways remains automatically at least equal to the thickness limit so asto provide these balloons with a practically absolute protection againstfire, meaning such risks as it is desired to guard against. It isapplicable to captive, free and dirigible balloons. It consistssubstantially in providing the 30 inner envelope and the outer envelopewith extensible contrivances judiciously chosen and in arranging thesetwo envelopes relatively to each other in such manner that under allcircumstances during the ascension, the space between the two envelopesis always at least equal to the thickness limit.

In particular the two envelopes are homothetic for a given condition oftheir inflation. In particular also, the extensible contrivances arearranged in such manner that the two envelopes remain homothetic in aconstant ratio, during the, variations of volume allowed by the freeplay of their elastic connections. In particular, again, the extensiblecontrivance of the outer envelope consists wholly or partly of theextensible contrivance of the inner envelope, vand vice versa. Finally,if the thickness limit is of a small absolute value, it may besuflicient to adopt an approximate method whereby the two envelopes areno longer strictly, but only approximately homothetic during theirvariations of shape without the protection required being therebydiminished.

The construction of extensible envelopes for balloons is founded, as iswell known, on the following principle :--The envelope consists ofpanels of impermeable material assembled according to the methods in usefor this kind of construction, but its outer surface is deformed by theuse of elastic connections. When such an envelope is 119 inflated. theelastic connections begin to stretch, the material assumes a shape andundergoes a superficial tension'which equilibrates the tension of theelastic connections. The gas is therefore slightly compressed andconsequently the shape of the envelope is regular and always the samefor an identical inflation. Fi'irthermore, if the introduction of gasinto the balloon continued, the" elastic connections become lengthened,the volume of the keel increases and the shape of the outer surface isaltered. The same phenomenon occurs when the balloon rises in altitudeand the surrounding pressure decreases. Inversely, when the balloondescends and the surrounding pres-- sure increases, the volume of theenvelope, due to the play of elastic connections, diminishes, whilstremaining all the same under pressure. Inall these motions, the mass ofgas contained in the envelope is constant. The total ascensional powerof the balloon is therefore kept constant, whilst losses of gas in theascensional movement are avoided. If furthermore the elastic connectionsare arranged in such manner that the centre of gravity of the volume ofthe keel remains the same during all the movements of extension andcontraction of said connections, it is known that great facility ofequilibration results therefrom, which makes it possible to give aconsiderable stability to the balloon.

forces ofaction andconsequently the exact shape of the surface, whichmeans that the shape varies with the volume, but is perfectly definiteat each instant.

Hence, if a balloon is constructed with a double .envelope consisting oftwo extensible envelopes,

inasmuch as, at every instant during the ascension, it is the same cause(surrounding pressure and. temperature) which influences these two keelsto produce their volume and therefore their external shape, it will bepossible to construct these two envelopes and to assign to themrespeotive positions which are such that at every instant and at allpoints their distance apart is at least equal to the thickness limit.

Generally speaking, it will be found an advan tags to choose for the twoenvelopes homothetic shapes in a ratio which is such that for thesmallest volume it is necessary to provide during the ascension (inprinciple at the moment of leaving the ground), the minimum space apartof the two envelopes is at least equal to the thickness limit. Iffurthermore the two extensible systems are such that the two envelopesbecome deformed, whilst remaining homothetic and in the same ratio, thedistance apart will vary in function of the volume. It will therefore becapable of only increasing during the ascension and hence it will alwaysbe at least equal to the thickness limit. This condition of constanthomothetic state of the two envelopes will be greatly assisted by towhich the protection under this patent will naturally have to beextended, as well as to apparatus in which the same process is used andto their detached elements. It will be easily understood with the aid ofthe following and the accompanying drawings which are of course given byway of non-limiting examples only.

Fig. 1 shows a transverse section of a balloon constructed according tothe system claimed.

Fig. 1 shows a detail View of part of Fig. 1 on an enlarged scale.

Fig. 2 shows a longitudinal section of Fig. 1.

Figs. 3 and 4 illustrate a transverse section and longitudinal sectionof another balloon which constitutes another example of construction.

A is the inner envelope which is filled with light gas; it belongs tothe trilobe type. Its transverse section consists of an equilateraltriangle with apices 1,2 and 3 and three equal arcs connected with saidapices (1, 6, 2)--(2, 4, 3) and (3, 5, 1). According to Fig. 2 thedifferent sections perpendicular to the axis 10-11 are at each pointsimilar to that in Fig. 1. The apices 1, 2 and 3 rest on curves (10,1,11)(10,2, 11) and (10, 3, 11) judiciously chosen, so as to give to theinflated keel a suitable shape. The envelope A is therefore formed byv avolume having the general shape of a triangular prism with curved edges,and three lobes resting on the three faces of said prismatic surface.The surface of the lobes is formed by panels of impermeable materialassembled in accordance with the usual methods for this kind ofconstruction. The sides of the triangle are formed on the contrary byelastic connections such for instance as sandows, that is multi-strandedshock-absorber elastic, 7, 8 and 9 on the whole or part of their length.The length of these elastics, when at rest,.before fixing and theirdistance apart, are regulated in such manner that they impart to thekeel a suitable pressure to use the balloon.

Around said envelope is arranged another envelope B which has a circularsection. It carries on each side and symmetrically with reference to thevertical plane containing the axis two expansible double pleats, eachformed by a hollow fold and having elastics in four planes, such as 12,13, 14 and 15 attached to the keel according to meridian lines of thesurface. Said elastics are not shown in Fig. 2, but only near thepoints,- the starting point of the meridian lines on which they rest.The space between the envelopes A and B is filled with inert gas and theconnection between these two envelopes is formed by a number of elasticconnections arranged according to the planes of symmetry of the lobes,such as 16, 17 and 18. These connections are calculated in such manneras to be moderately stretched when the balloon is inflated up to thevolume which corresponds to zero altitude. Furthermore, the distanceapart between the two envelopes is determined in such manner that forthe same degree of inflation,-it is, at each point, at least equal tothe thickness limit. The envelope B further carries the usualaccessories, planes, elevators, gondolas, suspension means etc., notshown in the drawings.

When the balloon rises, the surrounding pressure diminishes and thevolume of the two keels increases by the deformation of their outersurface. It is easy to perceive that in the case of the envelope B thehollow folds open and the section remains circular, but with aconstantly increasing radius. In regard to the keel A, the sides oftheequilateral triangle increase in length and the points such as 1, 2and 3 move away from the axis, whilst the points situated on the plane ssection is of the quadrilobe type.

of symmetry of the lobes such as 4, and 6, remain approximatelyinvariable. The volume of the keel increases because its sectionapproximates a circular section, but its outer overall space does notappreciably change. The minimum distance apart existing in the plane ofsymmetry of the lobes is therefore increasing. The maximum distancewhich existed on the outside of the re-entrant angle, is reduced, but itcan never be reduced below the thickness limit, inasmuch as the sectionof the keel A can never attain the circular. When returning to theground, the reverse phenomenon takes place; the two keels are reduced involume, but the distance apart can never fall below the thickness limit,inasmuch as for the zero altitude such distance apart is already atleast equal to the thickness limit. Automatic protection is thereforeassured.

A is the envelope with light gas; its transverse It is formed by asquare, having apices 21, 22, 23 and 24 and four circular arcs (21, 25,22)--(22, 26, 23) 23, 2'7, 24)--(24, 28, 21). According to Fig. 4 thedifferent sections perpendicular to the axis 29,

are at each point similar to that shown in 3. The apices 21, 22, 23 and24 rest on curves (29, 21, 30)-(29, 22, 30)-(29, 23, 30) (29, 24, 30)judiciously chosen so as to give to the balloon a suitable acre-dynamicshape. The envelope A is therefore formed by a volume having the general7 whole or part of their length. The length of said give to theenvelope. is provided another envelop-e B, the surface of connections,when at rest, and their distance apart are regulated in such manner thatthe tensions they produce on each element of len th should correspond tothe pressure it is desired to Around said first envelope which ishomothetic of the first relatively to the centre 0 of the figure at themaximum cross section. The transverse sections of said second envelopeare therefore similar to those of the keel A. The different elements arenumbered on the drawings by adding 20 to the figure which indicates thecorresponding elements of envelope A. The apices of the squares of thetransverse sections 41, 42, 43 and 44 therefore rest on the curves (49,41, )(49, 42, 50)(49, 43, 50) and (49, 44, 50), which in Fig. 4 arehomothetic of the corresponding curves of the keel A. In tie keel Bthere are no elastics forming the sides of the square section of theprism with a quadrangular base.

The connection between the two envelopes is ensured by elasticconnections such as 21, 41, 22, 42, 23, 43 and 24, 44 situated in thesymmetrical diagonal plane of the transverse section and preferablyattached to the fixation point of the sandow elastics of the keel A.These connections are not shown in Fig. 4.

The smallest distance between the envelopes is obviously in the sectionof the maximum cross section, at the nearest points of the homotheticcentre, that is to say in the re-entrant angles corresponding to theapices of the squares. The ratio of the homothetic position is to becalculated so that in the case of the smallest volume it may i bepossible to obtain for the balloon when rising the minimum distanceapart or a distance at least equal to the thickness limit.

The envelope B also carries the usual accessories, planes, elevators,gondolas, suspending means, etc., not shown in the drawings.Nevertheless, it is an advantage, in certain cases, to fix thesuspending means to the inner envelope, and allow them to pass throughthe envelope B through apertures, so as to reduce the resistance of theballoon in the wind.

When the balloon rises the surrounding pressure diminishes. Due to theplay of the elastic connection, the two surfaces become deformed, whilstincreasing in volume. The volume of the lreel A increases in inversratio proportional to the variation in pressure. The same applies to thekeel B and therefore also to the volume included between the twoenvelopes and corresponding to the volume B-A. If furthermore theelastic connections are judiciously chosen and if in particular they arelengthened proportionally to the loads they carry, it is obvious thatthe two surfaces will remain constantly homothetic and in a constantratio. But in this increase of volume, all the elastic connectionsbecome lengthened and the surface moves, so to speak, away from the axisand particularly to the re-entrant angles. The minimum distance apartbetween the two envelopes therefore also goes on increas in". In thelongitudinal direction there can be no appreciable displacement of thetwo keels relatively to each other, because if such a displacement tool:place, all the elastic connections provided between the two envelopeswould give components parallel to the axis which would at once bring thetwoenvelopes back to their respective positions.

To' sum up, if a value at least equal to the thickness limit has beengiven to the smallest interspace between the two envelopes, in thefurrows, at the height of the maximum cross section, for the smallestvolume, that may be reasonably considered under the conditions of theascension, it is certain that, in all the variations of volume whichtake place during the ascension, the distance apart at all points willalways be at least equal to the thickness limit, and consequentlyprotection will be assured.

In a number of cases of application, the thickness limit need not beconsiderable. On the other hand the total variation of volume of theheels, which depends on the conditions under which the balloon is used,is also in most cases rather small. Under these circumstances, thevariation in the length of the elastic connections between the twoenvelopes, such as 21, 4l'22, 42 etc., is very small. It is thereforepossible, in a number of cases, to replace said elastic connections bynon-elastic connect-ions as, for instance, strips of material cut out orassembled together like 49, 41, 50, 30,

21, 29, 49. In the variations of volume in the keel, due to the play ofthe connections of the elastic contrivanoe of the keel A, the twosurfaces no longer remain strictly homothetic, but only appreciably so.

etween the two surfaces in the region of the furrows 21, 41 remainsappreciably constant, but as this distance apart is, owing to itsconstruction, at least equal to the thickness limit, the protection isagain assured.

It remains quite clear that if an incendiary projectile passes throughthe balloon, the balloon will not catch fire, but the two envelopes willbe pierced. There will be an escape of gas and therefore a fall ofpressure, but so long as the elastic In particular, the distance apartconnections remain stretched, the homothetic form of the two envelopeswill be appreciably maintained. All the pilot will have to do is to stoprising before the damage to the envelope may have any serious resultupon landing. All the same, however, the main danger, namely fire, willhave been avoided.

In the case where the incendiary projectile may touch the balloontangenitally and pass through the outer envelope only, the intermediatespace between the two envelopes will become defiated through the inletand outlet apertures, but the inner envelope, due to the play of theelastic connections like 21, 22 will retain its form and pressure andthe material of the outer envelope Will become folded. It will then befor the pilot to decide whether he is to continue or not the ascensionwith an unprotected balloon, but here again fire with its seriousdangers will have been avoided.

It remains clearly understood that the probability of occurrences ofthis description as well as the time eventually necessary for landing,is to be taken into account in determining the thickness limit. Likewiseand due to the fact that the materials for balloons are not absolutelyimpermeable, the relative porosity of said materials may be taken intoaccount to determine the thickness limit. ihis porosity may also betaken into account when the balloon is inflated or refilled before theascension. If it is feared that owing to the much higher ratio of thesurface to the volume, the loss of inert gas should be greater than theloss of light gas, it is easy not to exactly fill up the envelope A and,for instance, to put the envelope B only under pressure. Under thesecircumstances, the tension of the elastic connec- 'tions of thecontrivance of the envelope A like 21,

22 will be transmitted entirely through the intermedium of connectionseither elastic or not, such as 21, 41 in the envelope B. As and when theloss due to the porosity of the material of the envelope B occurs, theenvelope A will progressively become stretched, whilst absorbing aportion of the tension of the elastic connections like 21, 22 Withoutthe envelope B becoming deformed. It will be sufficient to determinaatthe moment of the refilling of the balloon before the ascension andwhilst taking into account the relative porosity of the envelope A and Band the probable duration of the ascension, up to what point the normalinflation with inert gas must be exceeded, so that at the moment oflanding, the envelope B may still be under pressure.

It is self-evident that the examples above given are only given for thepurpose of clearly explaining the object of this invention and to showthe diversity of its possible applications, but they limit in no way thearrangements which can be realized by this invention. I I

What I claim and desire to secure by Letters Patent of the United Statesof America is:-

1. In an elongated non-inflammable balloon, the combination of an outerexpansible envelope, an inner expansible envelope inclosed within saidouter envelope, an inflammable lifting gas filling said inner envelope,an inert gas filling the space between said inner and outer envelopes, aplurality of extensible elastic tensile connections attached to each ofsaid envelopes for taking up the variations in volume of each of saidinner and.

outer envelopes, and tensile means for maintaining the relativepositions of the two envelopes, the expansibility of both outer andinner envelopes ensuring under all atmospheric conditions a protectivejacket of inert gas equal to or greater than a predetermined minimumsafe thickness.

2. A balloon as claimed in claim 1, in which the inner and outerenvelopes have a common axis and a common centre of figure at themaximum cross section.

3. A balloon as claimed in claim 1, in which the inner outer envelopeshave a common as well as a common centre of figure, and in which theenvelopes are homothetic relatively to the said centre.

4. A balloon as claimed in claim 1, in which the two envelopes haveextensible'elastic tensile connections comprising multi-strand'edelastic cords, for the purpose set forth.

5. A balloon as claimed in claim 1, in which.

the inner envelope in cross section has a plurality oi re-entrantangles, and in which the said re-entrant angles are interconnected byelastic deformable means, for the purpose set forth.

6. A balloon as claimed in claim 1, in which the inner envelope has incross section a plurality of ice-entrant angles which are interconnectedby elastic deformable means, whilst the outer envelope is attached tothe inner envelope by elastic means. i I

'7. A balloon as claimed in claim 1, in which the outer envelope isformed with two double pleats extending from end to end and havingelastic connections between portions of the pleats and the envelopearranged in a plurality of planes, for the purpose set forth.

8. A balloon as claimed in. claim 1, in which the two envelopes andtheir deformable means are such that the envelopes remain homothetic andin constant ratio during the variations of volume allowed by the elasticconnections in the envelopes.

JEAN LETOURNEUR.

